Nature of chemical states of sulfur embedded in atomic-layer-deposited HfO₂ film on Ge substrate for interface passivation

Sulfur was embedded in atomic-layer-deposited (ALD) HfO₂ films grown on Ge substrate by annealing under H₂S gas before and after HfO₂ ALD. The chemical states of sulfur in the film were examined by S K-edge X-ray absorption spectroscopy. It was revealed that the valences of S-ions were mostly -2 at Ge/HfO₂ interface (GeS_x or HfO_2-yS_y to passivate the interface), while they were mostly +6 in HfO₂ layers (sulfates; HfO_2-z(SO₄)_z). The leakage current density in post-deposi-tion-treated film was lower than that in pre-deposition-treated one. This suggests that the passivation of defects in oxide layer by sulfate ions is more effective to lower the leakage current rather than the interface defect passivation by S^2- ions.